1. Field of the Invention
The present invention relates to an internally meshing planetary gear structure particularly suitable for a reduction gear or a step-up gear requiring a high output with the small size, and a method for machining thereof.
2. Description of the Prior Art
The conventional internally meshing planetary gear structures have disclosed in, for example, Japanese Patent Laid-open No. sho 60-260737, U.S. Pat. No. 3,129,611 and the like. In such a gear structure, a casing is provided, and the tip of a main rotational shaft is inserted into the casing. A first and second supporting blocks are disposed around the main rotational shaft in an axially spaced apart manner. Also, the above supporting blocks are rotatably supported by the casing through respective bearings, and rigidly connected with each other through a carrier body. A plurality of eccentric body shafts are disposed along a circumference coaxial to the main rotational shaft. The above eccentric body shafts are rotatably supported at both the ends thereof by eccentric body shaft bearing holes formed on the first and second supporting shafts through eccentric body shaft bearings, respectively, and are rotated in an interlocking relation with the rotation of the main rotational shaft. Eccentric bodies are provided at the approximately axially central portions of the eccentric body shafts, respectively. Externally toothed gears are provided between the first and second supporting blocks, and eccentrically rotated around the main rotational shaft with the eccentric body bearing holes respectively formed thereon being fitted to the eccentric bodies through the eccentric body bearings, respectively. An internal gear is fixed on the casing for internally meshing with the above externally toothed gears.
FIGS. 10 and 11 shows the conventional internally meshing planetary gear structure of this type.
In these figures, numeral 1 designates a cylindrical casing. The casing 1 has an external flange 2. The tip of an input shaft (main rotational shaft) 3 rotated by a motor (not shown) is inserted into the central portion of the casing 1.
In the casing 1, a first supporting block 4 and a second supporting block 5 are oppositely disposed in an axially spaced apart manner. These first and second supporting blocks 4 and 5 are rotatably supported around the internal periphery of the casing 1 through bearings 6a and 6b.
The second supporting block 5 (in the right side in FIG. 10) has a carrier body 7 (see FIG. 11) having a complex shape and projecting to the first supporting block 4 (in the left side in FIG. 10). Both the supporting blocks 4 and 5 are rigidly connected to each other by bolts 29 and pins 30 through the carrier body 7 having such a complex shape, thus constituting a carrier as a whole.
Also, in the casing 1, three eccentric body shafts 8 are disposed in parallel to the input shaft 3. These eccentric body shafts 8 are circumferentially spaced at equal intervals on a circumference coaxial to the input shaft 3. Both ends of each eccentric body shaft 3 are rotatably supported in eccentric body shaft bearing holes 10a and 10b of the first and second supporting blocks 4 and 5 through eccentric body shaft bearings 9a and 9b, respectively.
The end portion of each eccentric body shaft 8 on the first supporting block 4 side projects outwardly from the portion supported by the eccentric body shaft bearing 9a. Three transmission gear units 13 are mounted on the projecting portion through splines 12. In this case, the transmission gear units 13 are respectively constituted of a pair of gears for preventing the backlash.
The first and second supporting blocks 4 and 5 are formed with center holes 14 and 15 at the radial centers thereof, respectively. The above input shaft 3 passes through the center holes 14 and 15. A pinion 16 meshing with the transmission gear units 13 fixed on each eccentric body shaft 8 is fixed at the tip of the input shaft 3. Accordingly, the rotation of the input shaft 3 is equally distributed to three eccentric body shafts 8 through the pinion 16 and the transmission gear units 13.
In this case, the teeth number of the each transmission gear unit 13 is specified to be larger than that of the pinion 16. Consequently, the rotation of each eccentric body shaft 8 is reduced in correspondence with the gear ratio between the transmission gear unit 13 and the pinion 16.
Two eccentric bodies 17a and 17b are axially lined-up at the approximately axially central portion of each eccentric body shaft 8. These eccentric bodies 17a and 17b are phase-shifted by 180.degree. to each other.
On the other hand, two disk-like externally toothed gears 18a and 18b, each having an outside diameter slightly smaller than the inside diameter of the casing 1, are axially lined-up between the first and second supporting blocks 4 and 5. Each of the externally toothed gears 18a and 18b is provided with three eccentric body bearings holes 19a and 19b, through which the above eccentric body shafts 8 pass respectively. The above eccentric bodies 17a and 17b are fitted to the eccentric body shaft bearing holes 19a and 19b through eccentric body bearings 20a and 20b, respectively. Accordingly, as shown in FIG. 11, the externally toothed gears 18a and 18b are supported in the state where the center Og thereof is eccentric to the rotational center Of of the input shaft 3 by a distance &lt;e&gt;. Thus, these externally toothed gears 18a and 18b are rotated in a rolling (swaying) manner by one rotation around the rotational center Of of the input shaft 3 for each rotation of the eccentric body shaft 8.
As the above eccentric body bearings 20a and 20b, needle bearings are here used. These eccentric body bearings 20a and 20b are axially positioned by stopper plates 21 and 23, and a flange 22 provided on the eccentric body shaft 8.
Each of the above externally toothed gears 18a and 18b has circular arc or trochoid shaped external teeth 24. An internal gear 25 meshing with the externally toothed gears 18a and 18b is disposed on the outer peripheral side of the externally toothed gears 18a and 18b. The internal gear 25 is formed integrally with the casing 1 around the inner periphery of the casing 1. This internal gear 25 has internal teeth constituted of outer pins 26. In addition, the outer pins 26 are secured by a pin pressing ring 27 from the inside for preventing the outer pins 26 from slipping off.
As shown in FIG. 11, insertion openings (inserting-fit holes) 28a and 28b, each having a complex curved contour, are formed at the central portions of the external gears 18a and 18b, respectively. The carrier body 7 of the second supporting block 5 passes through these insertion openings 28a and 28b. Thus, in the state where the end surface of the carrier body 7 is closely contacted with the inner end surface of the first supporting block 4, the first and second supporting blocks 4 and 5 are rigidly connected to each other by the bolts 29 and the pins 30, thereby constituting an integral carrier.
The carrier body 7 is intended to mutually transmit the rotational forces applied on the first and second supporting blocks 4 and 5. The insertion openings 28a and 28b of the externally toothed gears 18a and 18b has a size and a shape enough to prevent the interference with the carrier body 7 even in rolling (swaying) of the externally toothed gears 18a and 18b.
Now, the function of the gear structure will be described.
First, it is here assumed that the casing 1 is fixed, and the rotational output is taken from the carrier constituted of the first and second supporting blocks 4 and 5.
As the input shaft 3 is rotated, three eccentric body shafts 8 are rotated at an equal speed in the same direction (reversed to the rotational direction of the input shaft 3) through the pinion 16 and the transmission gear units 13. As described above, two eccentric bodies 17a and 17b are provided on each of three eccentric body shafts 8. Accordingly, the eccentric bodies 17a and 17b are eccentrically rotated at an equal speed in the same direction, so that two of externally toothed gears 18a and 18b are rotated in a rolling (swaying) manner around the input shaft 3.
In this case, since the casing 1 is fixed, that is, the internal gear 25 is fixed, the externally toothed gears 18a and 18b are rolled while internally meshing with the internal gear 25 in the state where the free rotation is restricted. For example, assuming that the teeth number of the externally toothed gears 18a and 18b are specified at N, and the teeth number of the internal gear 25 is specified at (N+1), the tooth difference is one. Accordingly, the externally toothed gears 18a and 18b are shifted (rotated on its axis) by one tooth with respect to the internal gear 25 for each rotation of the eccentric body shafts 8.
This shifting, that is, the rotations of the externally toothed gears 18a and 18b are transmitted to the first and second supporting blocks 4 and 5 through the eccentric body shafts 8. Since the supporting blocks 4 and 5 are integrated with each other through the carrier body 7, the rotational forces respectively transmitted to the supporting blocks 4 and 5 are combined, and taken from the supporting block 4 or 5 on the output side. In addition, the supporting blocks 4 and 5 are reduced at -1/N rotation for one rotation of the eccentric body shafts 8.
In the above, the function has been described assuming that the casing 1 is fixed and the output is taken from the side of the supporting block 4 or 5. However, the output may be taken from the casing 1 side, with the supporting blocks 4 and 5 being fixed. In this case, a counter-member is connected to the external flange 2 provided on the casing 1. With this arrangement, the reduced output is taken from the casing 1 side at the 1/(N+1) rotation and in the reverse rotation to the above case being taken from the side of the above supporting block 4 or 5.
Thus, the reduced rotational output may be taken from the side of the supporting block 4 or 5, with the casing 1 side being fixed, or may be taken from the casing 1 side, with the supporting blocks 4 and 4 being fixed. The above two types of the gear structures are adapted for reduction gears. In terms of the type of taking the output, the former is called as a carrier rotation type and the latter is called as a casing rotation type.
The conventional structure shown in FIG. 10 is assumed as the casing rotation type. Accordingly, a cover 31 is provided to the opening portion of the casing 1 on the side of the transmission gear units 13.
Incidentally, the gear structure of the casing rotation type or the carrier rotation type can be used as a step-up gear by reversing a relationship between the input and the output.
Next, the conventional gear structure of the carrier rotation type will be briefly described with reference to FIG. 12.
In the carrier rotation type, generally, an output shaft is provided integrally with the supporting block which is on the opposite side to the input shaft. Thus, the reduced rotational output is taken from the output shaft. However, in the conventional structure, the counter-member P on the output side is directly connected to the first supporting block 4. In this gear structure, the reduction mechanism is almost similar to that shown in FIGS. 10 and 11, except that the carrier body 7 for connecting both the supporting blocks 4 and 5 to each other is provided not on the second supporting block 5 but on the first supporting block 4, and the cover 31 is omitted. The main difference lies in that screw holes 32 are formed on the outer surface of the first supporting block 4, and thus the counter-member P is mounted by screwing bolts 33 in these screw holes 32.
In the above two gear structures, for connecting the first and second supporting blocks 4 and 5 to each other, there is used the carrier body 7 formed integrally with the first and supporting block 4 or the second supporting block 5. However, in U.S. Pat. No. 3,129,611, carrier pins (cage bars) are used in place of the carrier body 7 for connection. In each of the carrier pins, both ends thereof are rigidly fixed on the first and second supporting blocks (disks) for connecting both the supporting blocks, thus constituting a carrier (cage).
On the other hand, Japanese Patent Laid-open No. sho 63-22289 proposes the technique of improving the accuracy by simultaneous machining in the planetary gear structure of carrier rotation type disclosed in Japanese Patent Laid-open No. sho 60-260737. The technique in Japanese Patent Laid-open No. sho 63-22289 is essentially similar to that in Japanese Patent Laid-open No. sho 60-260737. Accordingly, the technique will be briefly described with reference to FIG. 10. In order to simultaneously machine eccentric body shaft bearing holes 10a and 10b formed on on respective sides of supporting blocks 4 and 5, and eccentric body bearing holes 19a and 19b on respective sides of externally toothed gears 18a and 18b, the diameters of the above bearing holes 10a, 10b, 19a and 19b are made to be identical to each other, and also the axes of respective holes are made in conformity with each other in the relative positional relationship (pitch circle diameter and pitch).
In recent years, a reduction or step-up gear using the internally meshing planetary gear structure of this type has been further strongly required to be reduced in size and enhanced in accuracy.
However, in the real situation, it has almost reached the limit in terms of the cost to meet the above requirement by enhancing the machining accuracy.
As described above, for example, in Japanese Patent Laid-open No. sho 63-22289, for simultaneously machining the eccentric body shaft bearing holes 10a and 10b on respective sides of the supporting blocks 4 and 5 and the eccentric body bearing holes 19a and 19b on respective sides of the externally toothed gears 18a and 18b, the above bearing holes 10a, 10b, 19a and 19b are made to be identical to each other, and the axes of respective holes are made in conformity with each other in the relative positional relationship (pitch circle diameter and pitch). Notwithstanding, this technique is insufficient to highly improve the machining accuracy.